Mercury Levels Predicted to Rise in Pacific Ocean Fish

Above: Bluefin tuna tends to have higher levels of mercury than yellowfin tuna. It also feeds deeper in the ocean.

As countries throughout Asia become increasingly reliant on fossil fuels, more harmful mercury is finding its way into the fish we eat. But new research suggests people can limit their mercury consumption by eating less fish that dwell deeper in ocean.

As countries throughout Asia become increasingly reliant on fossil fuels, more harmful mercury is finding its way into the fish we eat. But new research suggests one way people can limit their mercury consumption: Eat more fish that dwell near the ocean surface.

Scientists already know that large fish tend to ingest more mercury than smaller fish. The process of bioaccumulation accounts for how mercury gets amplified as it moves up the food chain. But they've also noticed something that couldn't be explained by bioaccumulation. Fish from darker, deeper waters often contain more mercury than similar fish feeding higher up.

Now, thanks to a new study co-authored by Brian Popp of the University of Hawaii, we now know why fish dwelling farther away from the ocean surface consume more mercury. It has to do with sunlight, which can actually help break up the harmful form of mercury that gets into fish — and onto our plates.

"Reactions catalyzed by sunlight break down that organic mercury," Popp said. Understanding this phenomenon could help guide regulators' seafood recommendations in coming decades, when mercury levels in fish are projected to spike.

Popp said, "If all things remain equal and there's a continued increase in emissions from power plants, projections show a two-to-three-fold increase over the next roughly 20 years."

He added that getting tough on rising mercury requires getting tough on emissions in Asia.